DESCRIPTION (from applicant abstract) The objective of this proposal is to investigate mechanisms of swallow gene function in Drosophila, as a means of understanding cytoplasmic organization and its role in early development. The swallow gene participates in the subcellular localization of two mRNAs during Drosophila oogenesis: bicoid and hu-li tai shao. swallow may also play a role in regulating nuclear divisions during early embryogenesis. The role of swallow in these processes will be examined by: 1)Characterization of the phenotype and molecular lesion associated with each of eight existing swallow alleles, 2) Identifying new alleles of swallow by mutagenesis screening, 3) Identifying genetic loci which interact with swallow via a deficiency screening protocol, and 4) testing models for swallow function using a transgenic approach. These studies are designed to answer some basic questions regarding swallow function. For example, are the localization of bicoid and hu-li tai shao RNAs governed by a single function of swallow? How is the function of swallow in oogenesis relate to its function in embryogenesis (if at all)? To what extent are the nuclear division aberrations observed in swallow mutants a consequence of a loss of hu-li tai shao mRNA localization, or are they rather a result of loss of swallow function? This research is of particular interest because it is becoming clear that many characteristics of subcellular localization are highl conserved. The subcellular localization of macromolecules is likely to be an important event in any cell which has an established polarity, and information gained from the proposed experiments will improve our understanding of subcellular organization in general.